OBSERVATORY

By HENRY FOUNTAIN

Published: January 11, 2000

Shrinking Iguanas

It's not that the marine iguanas of the Galapagos Islands are cheap, exactly -- but they do shrink in the rain.

That's the finding of two long-term studies of the lizards on two islands in the Galapagos chain, off Ecuador. The study, by a researcher from the University of Illinois and a colleague from Germany, found that some iguanas shrank by as much as two and a half inches, or about 20 percent of their body length, over two years.

That period coincided with El Nino events, when rainfall increased and food for the lizards, which forage for algae along the islands' rocky shores, was in short supply. The researchers found that iguanas that shrank more (as a percentage of length) survived longer than other iguanas during these lean times because they used less energy and their foraging was more efficient.

Since cartilage and connective tissue make up only about 10 percent of the total body length in these creatures, the shrinking can't be explained by decreases in these tissues alone. The researchers, who reported on their work in the journal Nature, believe that some bone is absorbed as well, and that steroids produced as a result of stress may be at least partly to blame, much the way astronauts' bones shorten slightly during long space trips.

But unlike humans (and any other adult vertebrates, as far as is known), the iguanas can lengthen once again when food availability improves and can switch between long and short repeatedly during their lifetimes.

Danger From Algae

Algae of a different sort played a much more draconian role among the sea life off California's central coast, according to researchers from the Monterey Bay Aquarium Research Institute and other institutions. They have connected the deaths of more than 400 sea lions in 1998 to an algal bloom that produced a powerful neurotoxin.

Mussels are often monitored during blooms for signs that the algae may be producing compounds that can be harmful to marine life or even humans. At the time of the 1998 bloom, however, no evidence of the neurotoxin, domoic acid, was found in blue mussels from Monterey Bay.

By contrast, high levels of the acid were found in bay anchovies. And, scientists report, high levels were also found in the urine and feces of surviving sea lions.

The survivors exhibited many symptoms of neurological damage, including seizures, head weaving and abnormal scratching. So it was not surprising, perhaps, that domoic acid produced by the algae was found to be the cause. But the Monterey Bay research, reported in Nature, is the first to conclusively link sea lion deaths to a harmful algal bloom.

The means by which the animals were poisoned was conclusively determined as well: eating the anchovies. That, plus the finding that mussels were unaffected, called into question the effectiveness of monitoring mussel toxicity alone during such blooms.

El Nino's Star Link

In the Andes of Peru and Bolivia, many farmers follow an old practice for determining when to plant their potato crops. They watch the stars of the Pleiades constellation in June, and the brighter the stars appear, the more rain they forecast for the growing season, October to May. If the stars are less bright and little rain is predicted, the farmers put off planting their drought-sensitive crop for several weeks.

Now, using weather data and satellite imagery, two American researchers suggest why this centuries-old method works. The visibility of the stars, the researchers report in Nature, appears to be an indicator of variability in the El Nino phenomenon.

In an El Nino event, the researchers say, high, wispy cirrus clouds become more abundant. These clouds are probably what makes the Pleiades appear less bright. So the dimmer stars foretell El Nino, when there will be less rain than normal in the Andes, and the rainy season will be delayed.